The present invention relates to heat exchangers and more particularly to improvements in plate type heat exchangers.
Many different types of heat exchangers are known for transferring heat to or from a fluid, usually transferring heat between two fluid media.
In almost all heat exchangers, the rate of heat transfer is of prime concern. This factor is of particular importance where heat exchangers are used in regenerative type gas turbine engines. Briefly, in such engines, waste energy of the hot gas stream exhaust is transferred, through a heat exchanger, to a pressurized air stream as it passes from the engine's compressor to its combustor. Thus the energy level of the hot gas stream generated in the combustor is proportionately increased to give an overall, theoretical, increase in engine cycle efficiency.
Heat exchangers for regenerative type engines, not only require a high rate of heat transfer, but also require a minimum impedance or pressure loss to the flow of the pressurized air and the hot gas streams therethrough. Otherwise, excessive pressure drops in either or both of the fluid flow paths could cause losses which more than offset the theoretical gains to be derived from the regenerative cycle. A factor of concern in such heat exchangers, is the wide range of temperatures encountered in cyclic operation and the resultant stresses that are induced in the component parts of the heat exchanger. The present invention is concerned with avoiding or distributing the stresses normally encountered when an annular plate-type heat exchanger is subjected to gradient heating, which stresses otherwise can result in the cracking of the plates and excessive pressure drops in either or both of the fluid flow paths.
Plate type heat exchangers, while having other applications, have been found particularly effective in fulfilling the needs described above for regenerative type gas turbine engines. A particularly effective heat exchanger of the is disclosed in U.S. Pat. No. 3,424,240. In that heat exchanger, a stack of corrugated plates, in the form of annular discs, define a central entrance for the hot gas discharge of the turbine engine. From this central entrance, the hot gasses pass radially outwardly between alternate pairs of plates to a discharge duct. Pressurized air from the engine compressor flows axially into inlet plenums extending longitudinally of the stack of plates, and then radially through cross flow paths between the plates, to axial exit plenums, also extending longitudinally of the stack of plates, back to the combustor of the engine. Reference is also made to improvement U.S. Pat. Nos. 3,785,435 and 3,831,674 relating to plate-type heat exchangers or recuperators of the general type which can be manufactured in modified form and assembled in accordance with the present invention to incorporate the improvements made possible by the present invention. Broadly, the present heat exchangers include companion pairs of relatively thin plates defining on their opposite sides, opposed portions of flow paths for first and second fluids. These plates are characterized by having first and second series of corrugations with one series being cross corrugations generally at right angles to the other.
The heat exchangers of the present invention and of the aforementioned Patents include pairs of plates peripherally welded to each other to form heat-exchange compartments therewithin, the plate pairs being welded to adjacent plate pairs at intermediate port or plenum areas to define the opposite bounds of the two fluid flow paths within the heat exchange compartments. One plate of each pair has a series of corrugations which are of the same spacing as and aligned with one of the series of corrugations of the other plate place. Further, the corrugations of the one plates are "out of phase" with corrugations of the other plate to define flow paths having longitudinal and cross sections which vary in area. Further, it is advantageous that one of the series of corrugations of the one plate have a lesser height than the other series of cross corrugations thereof and that the corrugations of the other plates are generally aligned with the lower series of corrugations of the one plate, as disclosed in U.S. Pat. No. 3,831,674 for example.
The pairs of first and second plates are formed as annular discs and are arranged in stacked relationship to define therebetween alternate flow paths for the first and second liquids. The intermediate ports or plenums are formed as longitudinal inlet and exit plenums which connect the heat-exchange compartments of the plate pairs for the introduction and discharge of the first liquid. As specifically adapted for use with a regenerative type gas turbine engine, the inlet plenum receives pressurized compressor air and the exit plenum discharges air to the combustor of the engine after the air passes through cross flow, heat exchange flow paths within the heat-exchange compartments of the pairs of plates. The second fluid is the hot gas discharge of the engine which passes through flow paths radial of the stacked discs, between the plate pairs and external to the heat exchange compartments.
The first and second plates, forming each plate pair, have flanges peripherally of their inner and outer diameters. The flanges of each first plate project in one axial direction and the flanges of each second plate project in the opposite direction towards and in matching relationship with flanges of the adjacent first plate. These matching flanges are respectively joined to form a heat exchange compartment to complete the cross flow paths for the pressurized air. Further, the longitudinal plenums are defined by intermediate flanged openings in the first and second plates. The surfaces of the adjacent first and second plates of plate pairs have flanged openings which are welded or joined peripherally of such openings so that the stack of plates becomes a bellows comprising a plurality of heat exchange compartments open to each other via the plenums for the compressed inlet air and the combustor exit air.